A pedal-driven scooter is typically composed of a fork and handlebars connected to hold a front wheel assembly linked to a back wheel assembly by means of a mainframe holding pedals and a transmission mechanism. Scooters are popular among users in crowded cities due to their small size when used, stored, and/or carried on. As scooters are generally used by riders in an upright position, they offer a riding experience closer to walking. They have higher maneuverability than bicycles when used in conditions where the interaction with pedestrian traffic requires many stops and turns. These advantages are achieved by using smaller wheels attached to a structure with a very low center of gravity. However, the use of small wheels comes in conflict with the need for high speed, and a mainframe closer to ground makes difficult the use of a traditional pedal and crank-set mechanism. One way of overcoming these difficulties is to use a stepper system which translates the up and down movements of the pedals within a limited angle range, into a continuous rotational movement that is further multiplied and transmitted to the back wheel by a transmission mechanism.
Examples of related art are described below:
U.S. Pat. No. 8,128,111 B2 pertain to a scooter that has a drive mechanism which is designed with two reciprocal pedals that transmit their up and down movements to a drive wheel by means of two linkage connections. A pedal needs to be positioned all the way up before it can be pushed back all the way down for the drive wheel to be able to perform a complete revolution. This design suffers from the well-known drawback of the conventional rotary pedal cranks where the driver has little control over the way the driving force is converted into drive torque at certain points of the pedal excursion. This arrangement makes the scooter difficult to ride uphill or on a muddy road, even when a speed change system is added. Moreover, this scooter has little possibilities to be folded efficiently, to be stored, or to be carried on when not in use.
U.S. Pat. No. 8,517,405 B2 pertain to a three wheel scooter with a reciprocal set of pedals and a gear train which translates the downward movement of one pedal into a rotational force directed to the back wheels, and also provides upward return force to a second pedal. The overall design of the scooter using this drive train has several drawbacks. The shafts of the two pedals are not collinear, causing discomfort for a rider who needs to hold one foot slightly ahead of the other foot when riding. Moreover, the pedals are designed to be pushed forward, thus the horizontal length of the scooter cannot be reduced, as would be the case with a scooter where the pedals are pushed backward, moving up and down on the sides of the back wheel. The two back wheels are rigid, thus prone to tip the scooter over at sharp turns. The angle range is not wide enough, thus limiting the speed the scooter can achieve.
Both U.S. Pat. No. 6,367,824 B1 and U.S. Pat. No. 6,817,617 B2 pertain to designs for tricycles with two front wheels using a well-known parallelogram structure which changes the inclination angle of both front wheels by the same amount as the inclination angle of the back wheel. The steering systems employed here use a tie rod arrangement, which works satisfactorily when the distance between the two front wheels is large enough not to matter at higher inclinations, where the two tie rods cannot be maintained collinear. However, this tie rod design cannot be employed for smaller tricycles or scooters, where the two front wheels are smaller in size and placed closer to each other. Consequently, at higher inclinations, or when one of the wheels runs over an obstacle while the other remains on the pavement, the two left and right tie rods pull the front tips of the wheels towards each other, thus breaking Ackermann's steering geometry rules.
None of the art described above addresses all of the issues that the present invention does.